Spray dryers are well known in the art for drying pharmaceutical and nutriceutical active agents and excipients. In general, a spray dryer is used to process fluid materials into powders. Typically, the fluid material is introduced into the spray dryer in the form of a solution, suspension, emulsion, slurry, or thin paste. In operation, the fluid material is fed from a feed delivery system to an atomizer. The atomizer disperses the fluid material into the drying chamber in fine droplets. A heated air supply applies heated air to the fine droplets in the drying chamber, causing the fine droplets to be dried into a powder, the powder being collected in a collection system. Spray dryers are widely used in the preparation of active agents. For example, it is known to spray dry an active agent in the form of a fluid material (for example, a liquid herbal extract) to form a powder, and thereafter, to blend the powder with conventional tableting agents, and then compress the resulting mixture into a tablet.
Examples of such tableting agents include lubricants, diluents, binders, disintegrants, and direct compression vehicles. Lubricants are typically added to avoid the material(s) being tableted from sticking to the punches. Commonly used lubricants include magnesium stearate, stearic acid, sodium stearyl fumarate, hydrogenated vegatable oil, and calcium stearate. Such lubricants are commonly included in the final tableted product in amounts of less than 1% by weight. Diluents are frequently added in order to increase the bulk weight of the material to be tableted in order to make the tablet a practical size for compression. This is often necessary where the dose of the drug is relatively small. Binders are agents which impart cohesive qualities to the powdered material(s). Commonly used binders include starch, and sugars such as sucrose, glucose, dextrose, and lactose. Typical disintegrants include starch derivatives and salts of carboxymethylcellulose. Direct compression vehicles include, for example, processed forms of cellulose, sugars, and dicalcium phosphate dihydrate, among others. Microcrystalline cellulose is an example of a processed cellulose that has been utilized extensively in the pharmaceutical industry as a direct compression vehicle for solid dosage forms.
Silicified microcrystalline cellulose is a particularly useful direct compression vehicle. Silicified microcrystalline cellulose is a particulate agglomerate of coprocessed microcrystalline cellulose and from about 0.1% to about 20% silicon dioxide, by weight of the microcrystalline cellulose, the microcrystalline cellulose and silicon dioxide being in intimate association with each other, and the silicon dioxide portion of the agglomerate being derived from a silicon dioxide having a particle size from about 1 nanometer (nm) to about 100 microns (μm), based on average primary particle size. Preferably, the silicon dioxide comprises from about 0.5% to about 10% of the silicified microcrystalline cellulose, and most preferably from about 1.25% to about 5% by weight relative to the microcrystalline cellulose. Moreover, the silicon dioxide preferably has a particle size from about 5 nm to about 40 μm, and most preferably from about 5 nm to about 50 μm. Moreover, the silicon dioxide preferably has a surface area from about 10 m2 g to about 500 m2/g, preferably from about 50 m2 /g to about 500 m2/g, and more preferably from about 175 m2/g to about 350 m2 /g. Silicified microcrystalline cellulose, and methods for its manufacture, are described in U.S. Pat. No. 5,585,115, the entire disclosure of which is hereby incorporated by reference. Silificified microcrystalline cellulose is commercially available from Penwest Pharmaceuticals, Inc., under the trademark Prosolv®. Prosolv is available in a number of grades, including, for example, Prosolv SMCC 50, Prosolv SMCC 90, and Prosolv HD.